For ultrasonic testing of workpieces, EP-A-O 232 794, DE-A-25 35 019, GB-A-2 068 550, and DE-A-29 30 508 call for the centering of the workpiece in an acoustic irradiation device centering of the workpiece in an acoustic irradiation device using a gas or fluid cushion. In this connection, e.g., DE-A-25 35 019 or GB-A-2 068 550 also calls for rotating spherical workpieces during acoustic irradiation.
In the manufacture of receptacles, it is frequently necessary, before or after they are filled and, if appropriate, sealed, to check various parameters, e.g., to look for the presence of hairline cracks in the receptacle walls, to check the fill level, the dimensional accuracy of the receptacle, etc.
The inspection processes used in this connection are referred to as scanning processes because a measurement window is always moved along the receptacle wall.
The term "vials" is used to refer to receptacles that are used in particular for pharmaceuticals or medications. They consist essentially of cylindrical glass container bodies that are closed with rubber plugs and whose edges are sealed to the container necks with metal collars. For example, vaccines are drawn from such receptacles by stabbing the injection needle through the rubber plug without breaking the seal on the vial.
This invention pertains in particular to the scanning inspection of such receptacles but can also readily be used for other rotationally symmetrical receptacles in order to check any of the parameters indicated below.
This description is based hereinafter on the preferred vial example, but without prejudice to its applicability to other receptacles.
In the case of the above-mentioned vials, there is a need, particularly after they are filled and sealed, to check the glass wall of the receptacle body for microcracks and/or to check whether the receptacle body is within prescribed dimensional tolerances. The inspection of the above-mentioned dimensional accuracy and the checking for the presence of microcracks in the receptacles call for an all-around inspection of the receptacle such as by scanning inspection. Even if the specified dimensional tolerances are observed, however, as regards their cylindricity such receptacles exhibit relatively large tolerable deviations in roundness from copy to copy; to a very large extent this makes it impossible to determine the geometrically exact location of their axis of rotation.
When performing all-around inspections of such receptacles, however, the obvious approach is not to move the inspection device around a stationary receptacle but rather, specifically because these receptacles are at least approximately rotationally symmetrical, to place the receptacles in front of a fixed inspection device and rotate them to perform the all-around inspection.
It would be possible to attempt to rest the above-mentioned approximately rotationally symmetrical receptacles on roller with axes of rotation essentially parallel to surface lines of the cylindrical receptacles, rotate them, and check the receptacle walls and their fill levels using, in particular, a non-contact inspection device such as a line camera, laser transmission or reflection units, photoelectric barrier units, etc. In this process it would be found that, particularly due to the lack of circularity that is still within tolerance, the mechanically defined placement of the container cylinder wall on rollers leads to inspection results that are at least only conditionally reliable.
An object of this invention is therefore to create a corresponding inspection process and a corresponding inspection device which can be used to obtain reliable inspection results on receptacles of the above-mentioned type despite relatively large shape-dimension tolerances.
For this purpose, the process of the invention is a process for scanning, particularly cylindrical receptacles, comprising arranging a receptacle on an air bearing along its surface line and rotating the receptacle essentially around it axis, and checking the receptacle with the aid of a scanning device that is kept stationary with respect to the rotational motion of the receptacle. An inspection device according to the invention for rotationally symmetrical receptacles, particularly cylindrical receptacles, comprises an air-cushion mounting for the surface line of a receptacle with compressed air discharge for bearing air; a rotation drive for the air-cushion-mounted receptacle; and a scanning unit for the receptacle. The preferred use of the above-mentioned process and device is for inspection of transparent glass receptacles, particularly vials for the presence of wall hairline cracks and/or dimensional accuracy.
Because, according to the process, the receptacles rest on air cushions along their surface lines and are rotated essentially around their axes of rotation, the installed air pressure of the cushion ensures that the receptacle is kept symmetrical owing to an equilibrium of forces at the receptacle wall, i.e., the receptacle is kept symmetrical relative to its outer surface, thus ensuring that a deviation from circularity, which by itself is entirely tolerable, is compensated optimally; this pertains to the "wobbling" of the outer wall during the rotation of the receptacle: rotation takes place without a defined axis position.
Preferably, the air cushion is essentially arranged around the surface line of the rotationally symmetrical receptacle, thus optimally ensuring the above-mentioned symmetry of the radially acting forces on the surface line.
With allowance for the fact that the dynamic air bearing of the type mentioned (which is understood to include, if appropriate, a bearing with another bearing gas as well), the rate of low of the air in the bearing gap leads to an underpressure there and a receptacle will be pushed against the bearing shell, but it is entirely possible to arrange (the receptacle) along a surface line which encompasses an angle of less than 180.degree..
In order to avoid at least partially disrupting the above-mentioned peripheral arrangement due to the action of a rotational drive, e.g., a mechanical frictional action on the receptacle surface line, in another preferred embodiment of the process a rotation-drive action for the receptacle is provided on the receptacle base, preferably in an approximately axial direction.
In this connection, in another preferred embodiment the optimization of the symmetrical arrangement of the air cushion, which can take effect on its own, is directly exploited owing to the fact that the above-mentioned rotation drive action, which is preferably applied at the receptacle base, occurs elastically at least in the radial direction, thus making allowance for the fact that no axis of rotation actually exists at the receptacle.
Preferred embodiments of the device of the invention, with the advantages just discussed in connection with the process, involve the use of an air-cushion bearing mounting which has a pair of bearing shells that are clamped against one another by springs. The rotation drive for the air-cushion-mounted receptacle has a drive shaft which acts on the receptacle base essentially coaxially, and can thus be brought into frictional contact with the receptacle base. The drive shaft is elastic at least in the radial direction, preferably at the end.
The device further includes an inspection unit, particularly a scanning unit. A relative drive is provided in order to displace the receptacle with respect to the inspection unit essentially parallel to the approximate axis of rotation of the receptacle. In such case the inspection unit is preferably a line camera, laser unit, or photoelectric barrier unit for transmission or reflection measurement.
The process of the invention and the device thereof are particularly suitable for the inspection of vials, and most particularly during their in-line accumulation in production. More basically, however, this process and device are suitable for the inspection of rotationally symmetrical glass receptacles, as well as, if appropriate, for the inspection of rotationally symmetrical receptacles that are made of other, non-transparent materials, e.g., for checking whether form-dimension tolerances are observed or not. Due to the low-friction air-cushion arrangement, receptacles can be rotated at high speed, thus making it possible to conduct the inspection quickly and therefore extremely economically.
The invention is explained below with reference to the figures.